# What power supply should I use?

I am building a robotic arm using 8 servo motors. I am wondering about what voltage my external power will need to be to control all of them at 6v. I am wanting to use a rechargeable battery.

I am wondering about what voltage my external power will need to be to control all of them at 6v

Well that would be 6V then wouldn't it?

You're asking the wrong question. The question you should be asking is:

How much current will I need from my 6V power supply?

Add up the total current required by all of the devices and that is the minimum current the PSU has to provide

On top of that you need to consider how long the supply should last. The average current need to draw from the batteries, multiplied by the number of hours you need it to run for, is the minimum capacity of battery you need.

For instance, if you need to draw an average of 500mA for 6 hours then you need (0.5*6 =) 3Ah (or 3000mAh) batteries (or better).

• It's not quite that simple as the loads will be highly variable, and the goal is a battery pack. Fortunately, RC servos are designed to run on 4 NiCd cells, and those handle high temporary current from moving stalled servos pretty well. So pack sizing is really more about how long it needs to work. The question for the MCU is then a distinct supply, running it at 3.3v or so to leave headroom for dips under load, or a boost converter. Aug 31 '16 at 4:36
• You may wish to consider how long youre using the rechargable battery. Basically ,since youre using rechargables you may want to consider how frequently you will need to recharge your batteries, the more electrical power your using at once (e.g. every second) the quicker your battery will run out and thus you may need to recharge it more. Aug 31 '16 at 18:55

You should use a Voltage Regulator for a stable Voltage Output.

First you should know your maximum Current consumption. Lets say for example maximum 2A.

You want the Voltage of the Servos stable, so they dont jerk around when there is a voltage drop or change. Because of this reason you should use a Voltage Regulator. For this example, choose one which has a Output of 6V 2A.

For the most of the Voltage Regulators you will be safe if you calculate an extra of 2V for the Voltage Drop. The Voltage Drop Value is specific for every Voltage Regulator Model. You can find this Value in its Datasheet.

So you would need a Power Source, for example a rechargeable NiMh battery with 8V(6V+2V), which can supply 2A. Not all batteries in the world will be able to give you 2A, but like all of the NiMh batteries should.

You can find the exact circuit for your Voltage Regulator in its Datasheet, which most likely also will have some (optional) capacitors in it.

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